The use of an inflatable cuff to occlude blood flow into a subject""s limb, thereby providing a bloodless surgical field in the portion of the limb distal to the cuff over a period of time suitably long for the performance of a surgical procedure, is well known in surgical practice. Tourniquet systems typically include an inflatable cuff for encircling a limb at a selected location and a tourniquet instrument for maintaining the pressure in the cuff near a selected pressure. Such tourniquet instruments of the prior art typically contain, or connect to, a source of pressurized gas and include a pressure regulating mechanism for controlling and maintaining the pressure of the gas supplied to the tourniquet cuff near the selected pressure. Typically a variety of cuff sizes are provided so that a cuff that overlaps itself when encircling the limb may be selected, thereby ensuring that pressure is applied to the limb around its entire circumference. Cuffs are also provided in a variety of shapes, widths, materials, configurations and other physical characteristics as required for different types of patients, limb locations, and surgical procedures.
Some types of tourniquet cuffs of the prior art have relatively complex physical characteristics aimed at safely and effectively occluding blood flow without regard to the cost of manufacture and although relatively effective cannot be manufactured at low cost, especially in small volumes. Other types of prior-art cuffs have simplified physical characteristics that reduce the cost of manufacture but that may not result in the safe and reliable occlusion of blood flow. No low cost, commercially available tourniquet cuff is known in the prior art that allows identification of the type and physical characteristics of the cuff by a tourniquet instrument to which the cuff has been pneumatically connected.
Modern prior art tourniquet instruments employ digital electronic technology in the regulation of pressure and in the detection of certain hazardous conditions. However the selected pressure for the tourniquet cuff is often based on the surgeon""s estimate of the minimum pressure required to safely occlude blood flow past the cuff. This minimum safe pressure is affected by the physical characteristics of the cuff, and so providing a convenient and reliable means of identifying certain physical characteristics of the cuff (such as length, width, and type) may be useful for a variety of functions. For example, if a wide cuff is being used, the instrument may display instructions to the surgeon to select a lower tourniquet pressure setting to reduce the chance of pressure related injury while still stopping blood flow effectively. Identification of the cuff also allows optimization of various operation parameters and hazard warning criteria of the tourniquet system. For example if a pediatric cuff is in use, the maximum allowable pressure supplied by the instrument may be reduced accordingly.
If the cuff type can be identified, a record may be kept more easily and more accurately for inventory control and optimization purposes. Such a record may also be used (in combination with recording of other parameters such as pressure used) to aid in establishing safer practice guidelines for the use of surgical tourniquets. Finally, a tourniquet system having automatic cuff identification enables sale or lease of the instrument to a user on a per-use basis or in connection with the purchase of specified quantities of the matching cuffs. A variety of related functions are enabled by an automatic cuff identification feature. For example if an inappropriate cuff is connected, the system may be programmed to warn the user and record the event, but function normally. The cuff identification and recording ability enables the system to be programmed to function with an inappropriate cuff up to a specified number of times only (with associated warnings), then subsequently be disabled unless an appropriate cuff is used.
In many cases, cuffs are color coded to indicate size. For example the xe2x80x98Comforter(trademark) Disposable Gel Cuffxe2x80x99 sold by DePuy Orthopaedics Inc. has a color dot on the outer packaging label corresponding to the cuff size, but no indication of cuff size on the cuff itself. In several other types of tourniquet cuff (for example xe2x80x98Zimmer ATS Disposable Tourniquet Cuffsxe2x80x99, Zimmer Patient Care, Dover, Ohio), components permanently attached to the cuff (such as edge trim and/or tie ribbon) are made of a selected color of material corresponding to the cuff size. These identification means are solely visual and interpretable by the user who is familiar with the color coding scheme. No communication to the instrument is established and therefore no automatic recording, display of information, or adjustment of instrument operating parameters relative to the cuff type can be done.
In U.S. Pat. No. 4,605,010, McEwen describes a tourniquet cuff that includes an electrical means for identifying remotely the physical characteristics of the cuff, as well as for remotely determining the circumference of the limb encircled by the cuff. To permit remote identification of cuff type, the McEwen ""010 cuff includes electrically conductive components within the cuff structure, and requires an electrical connection as well as a pneumatic connection between the tourniquet cuff and the tourniquet instrument. Thus electrical power and an electrically conductive pathway are necessarily present within the cuff, in close proximity to the patient""s limb encircled by the cuff. This can present a hazard to the patient under some circumstances. Also, inclusion of electrical components within the tourniquet cuff increases the cost and complexity of manufacture of such cuffs. The prior art tourniquet cuff described by McEwen ""010 also includes means for allowing a connected tourniquet instrument to remotely determine the circumference of the limb encircled by the cuff. This permits the tourniquet pressure setting to be adjusted, based on the relationship between the physical characteristics of the remotely identified cuff and the remotely identified circumference of the limb encircled by the cuff. No other tourniquet systems in the prior art known to the inventors of the current invention establish a connection other than a pneumatic connection between the cuff and the instrument, such that information about the cuff can be received by the instrument.
Certain tourniquet cuffs of the prior art, known commonly as disposable tourniquet cuffs, are designed and manufactured specifically for use in a sterile surgical field. In many cases such disposable tourniquet cuffs are sterilized after manufacture, are supplied as sterile products, and are discarded after one surgical procedure has been completed. Other tourniquet cuffs of the prior art, known commonly as reusable cuffs, are designed and manufactured for use in multiple surgical procedures. Such prior art reusable cuffs are generally supplied as non-sterile products, and are intended to be thoroughly cleaned and inspected before each surgical procedure. These non-sterile, reusable tourniquet cuffs of the prior art are discarded if inspection before use results in the detection of excessive wear, physical deterioration, or contamination.
The most commonly used cuffs in the prior art typically include three layers of material and a stiffener (Zimmer ATS Disposable Tourniquet Cuffs, Zimmer Patient Care, Dover, Ohio). The inner and outer layers are typically woven nylon coated on one side with thermoplastic polyurethane, the middle layer is plain thermoplastic polyurethane sheet, and the stiffener is made of high density polyethylene sheet. When encircling the patient""s limb in use, the inner layer lies against the skin. All three layers are die cut to a particular shape defining the length and width of the cuff, and all have the same perimeter. In a first sub-assembly operation, a port made of thermoplastic material is bonded to the middle layer, creating a gas passageway through the layer that a pneumatic hose may be attached to. In a second sub-assembly operation a reinforcing patch is bonded to the outer layer. In a third sub-assembly operation hook and loop fastening materials are sewn to the outer layer (thus rendering the outer layer gas permeable and therefore unsuitable for forming an inflatable portion of the cuff). The inner layer, middle layer with port, stiffener, and outer layer sub-assembly are then manually loaded into a die, aligned, and a press-type radio frequency (RF) sealing operation used to join the layers in a continuous gas-tight seal around the perimeter of the cuff. This results in a cuff with an inflatable bladder between the inner and middle layers, which can be inflated and deflated via the port, and a stiffener lying in the non-inflating space between the middle and outer layers. With this construction the stiffener is narrower and shorter than the bladder and lies inside the inner perimeter of the bladder-forming seal, so that the seal joins three layers of constant thickness materials around its entire perimeter. To create a smooth, rounded edge along the perimeter of the cuff that will not chafe the patient""s skin, an edge trim of nylon ribbon material is folded over the edge of the cuff around the perimeter of the cuff and sewn in place. Finally a nylon tie ribbon is sewn to one end of the cuff and an identifying label is sewn to one end of the hook-type fastening strap.
The tourniquet cuffs known in the prior art as described above have a relatively high cost of manufacture because the manufacturing process is relatively labor intensive. Also, to maintain a consistently high quality of manufactured product and thus reduce the rate of sub-standard products rejected during manufacture, these prior art tourniquet cuffs must be made by staff who have a relatively high level of training, skill and experience. These prior art cuffs are not well suited for a flexible manufacturing process in which different sizes of tourniquet cuffs are manufactured in small batches and rapid changeover from one type of cuff to another is possible. Finally, the maximum length of cuff that can be manufactured is limited by the sizes of the various die cutting and RF sealing equipment available. These limitations of the prior art are described in more detail below.
For each of the three RF sealing stages described above, an operator must load the individual layers of material into an RF sealing die in the correct order, alignment and orientation, activate the RF press for approximately 5 seconds, and then unload the die manually. Improper positioning of any one of the layers or the stiffener (for example if an edge of the stiffener encroaches into the RF sealed area around the perimeter of the cuff) may cause failure of the cuff. Before the final RF seal operation, a skilled operator must sew two separate pieces of hook and loop fastener material to the outer layer sub-assembly. These components must be centered between and parallel to the cuff sides and the stitching must be continuous and accurately positioned (particularly where it passes through the reinforcing patch) or a potentially hazardous structural failure may occur when the cuff is inflated. Because each cuff size and type has a unique perimeter, each requires a unique cutting die and certain unique RF sealing dies, fixtures, and press setups. Cuff length is limited by the table size of the die cutting and RF sealing equipment, and also by the length of RF sealing die that can produce a constant thickness seal along the entire length of the cuff.
After the final RF seal operation, the available width for sewing the tie ribbon and edge trim in place around the cuff perimeter (distance between the outer perimeter of the seal forming the inflatable bladder portion of the cuff and the outermost edge of the cuff material) is typically only 0.38 inches. Sewing the edge trim and tie ribbon in place is therefore particularly labor intensive and skill dependent because any encroachment of the stitching into the inflatable bladder portion of the cuff may cause the cuff to leak or burst when inflated. Conversely if the sewn joint passes outside the cuff material perimeter the edge trim or tie ribbon will not be securely attached in that area. Increasing the 0.38 inch width, thereby increasing the overall cuff width and length for a given inflatable bladder size, presents a safety-related problem because it is well established in the surgical literature that if all other design parameters are the same, the widest possible bladder width within a given overall cuff width will result in the lowest tourniquet pressure being required to stop blood flow past the cuff. Lower cuff pressures are desirable surgically because lower pressures are correlated with lower probabilities of injury to the limb encircled by the cuff. Alternatively stated, it is well established that a reduced bladder width within a given overall cuff width requires the use of higher tourniquet pressures to stop blood flow, and higher pressures are associated with higher probabilities of patient injury.
Tourniquet cuffs described by Guzman in European patent application EP1016379A1 and in commercial products manufactured in accordance with its teachings (xe2x80x98Comforter(trademark) Disposable Gel Cuffxe2x80x99, DePuy Orthopaedics Inc) include an inner layer material having a soft, felt-like surface lying against the limb. Along certain edges of the cuff the perimeter of the inner layer extends beyond the perimeter of the remaining layers and is folded over the edges of the remaining layers, thereby creating a rounded edge of soft material along the edges and protecting the patient from chafing. The folded-over edges are held in place by stitching lying outside the perimeter of the seal forming the inflatable bladder portion of the cuff, in a similar fashion to the edge trim attachment method used in the prior art Zimmer cuffs described above. Although the folded over edge arrangement eliminates the separate edge trim component used in the Zimmer cuffs, it suffers from the same disadvantages described in the preceding paragraph concerning labor intensiveness, skill dependency, and overall cuff width for a given bladder width.
In U.S. Pat. No. 4,979,953, Spence describes a tourniquet cuff with an edge trim sewn through the inflatable bladder seal, rather than outside the perimeter of the bladder seal. Although this arrangement may allow a wider bladder for a given overall cuff width and seal width compared to the Zimmer and DePuy cuffs described above, there is even less margin for error in the edge trim installation procedure because the stitching runs even closer to the inner perimeter of the inflatable bladder seal. Using a wider seal to overcome this problem (for example 0.50-1.0 inches as suggested by Spence in the ""953 patent) results in a narrower bladder width and correspondingly higher required cuff pressures and risk of pressure-related injury to the patient. Seal widths range from 0.13 inches to 0.25 inches in commercially available tourniquet cuffs known to the inventors of the current invention.
Certain tourniquet cuffs of the prior art do not have edge trim or folded edge as described above. This reduces the cost of cuff manufacture and simplifies the manufacturing process but may introduce a hazard when such a cuff is applied to the limb of a patient. For example in the tourniquet cuff described by Spence in U.S. Pat. No. 5,733,304 and in commercial products manufactured in accordance with its teachings (xe2x80x98Color Cuff IIxe2x80x99 sterile disposable tourniquet cuffs, InstruMed Inc., Bothell Wash.) the bond between the inner and outer layers extends to the outer perimeter of the cuff, presenting a stiff, sharp edge that could contact the patient""s skin and cause injury. Accordingly a separate limb protection means, such as the stockinette sleeve supplied with the xe2x80x98Color Cuff IIxe2x80x99, may be necessary to protect the limb from injury near the edge of the cuff and thus assure an adequate level safety for the patient. The need to use a separate limb protection sleeve in conjunction with such prior art cuffs adds an additional cost for the user and offsets the lower cost of cuff manufacture of such cuffs. Similarly the tourniquet cuff described by Robinette-Lehman in U.S. Pat. No. 4,635,635, commercial products manufactured in the past in accordance with its teachings (xe2x80x98Banana Cuffxe2x80x99 sterile disposable tourniquet cuffs, Zimmer Arthroscopy Systems, Englewood Colo.), and the tourniquet cuffs described by Eaton in U.S. Pat. No. 5,413,582 do not have edge trim and the sharp edges of the cuff may present a hazard to the patient. In U.S. Pat. No. 5,193,549 Bellin describes a cuff made of a sheet of material folded in half and sealed along the resulting three edges to form a bladder, in which the folded edge is not sharp but the three sealed edges are sharp and do not have an edge trim. In U.S. Pat. No. 5,411,518 Goldstein describes a cuff similar to the Color Cuff II and additionally including a separate border material applied around the perimeter of the cuff and a separate pad to be used with the cuff to protect the patient""s skin, thereby suffering from the disadvantages of increased manufacturing complexity and cost as discussed above. No prior art tourniquet cuff is known to the inventors of the current invention in which two strips of material form the inflatable bladder (allowing a low-cost continuous manufacturing process) wherein at least one of the longitudinal edges is further formed into a soft, rounded shape and is held in this shape by the seal forming the inflatable bladder of the cuff, thereby reducing cost by eliminating additional edge trim components and attachment operations.
Tourniquet cuffs of the prior art generally include a thermoplastic port permanently attached to the inflatable bladder allowing attachment of a pneumatic hose for pressurizing the cuff. Prior art ports consist of a planar flange that is RF sealed to the wall of the inflatable bladder and a cylindrical body portion extending out of the bladder in a radial direction away from the limb. A gas passageway passes through both the body and the flange to the bladder. Under certain circumstances the gas passageway may be blocked by the flexible material of the bladder lying against the planar flange, for example if the patient""s weight is pressing down on the port. This may lead to a condition in which pressure remains in the cuff after the surgeon has deflated it and the instrument indicates zero pressure, or a condition in which the cuff does not reach full pressure as indicated on the instrument. Both conditions may be hazardous to the patient.
To minimize the chance of pneumatic hoses encroaching on the surgical field distal to the cuff, many prior art ports have a 90 degree bend in the body portion and an extension of the body pointing proximally beyond the perimeter of the flange. Hoses connected to the port will therefore run in a proximal direction (away from the surgical field) and lie flat against the patient""s limb. Such ports suffer from the same risk of blockage as described above. In addition they complicate the cuff manufacturing process because the extended portion of the body must be manually passed through the hole in the bladder wall, then turned 90 degrees such that the flange portion lies parallel to the bladder wall. In order to form an uninterrupted gas tight seal between the flange and the outer layer, the RF sealing die must be recessed and the port and bladder wall assembly must be manually passed through the recess before sealing. In all prior art tourniquet cuffs known to the inventors of the current invention, the port flange surface inside the inflatable bladder is substantially planar; none have any provision for preventing blockage by the opposite bladder wall.
Tourniquet cuffs of the prior art generally include a stiffener cut from a sheet of flexible plastic material (such as high density polyethylene) to constrain the inflatable bladder portion of the cuff and thereby direct expansion of the bladder inwardly towards the limb when the cuff is inflated. The stiffener must therefore lie outside the inflatable bladder (for example in a non-inflating sheath as in the Zimmer cuffs described above) or otherwise lie against the outer layer of the bladder when the cuff is inflated. Some tourniquet cuffs in the prior art (Oak Medical, Briggs, North Lincs, UK, and described by Eaton in U.S. Pat. No. 5,413,582) consist of two layers only, wherein the outer layer is a gas impermeable stiffener material of constant thickness and stiffness extending across the entire cuff width. As described by Eaton in the ""582 patent, this arrangement can allow a continuous manufacturing process in which the two long strips of material are extruded and joined along the edges, then cut to length and sealed across each cut ends to form an inflatable bladder. However due to the uniform thickness and stiffness of the outer layer, the inner layer must stretch and/or the outer layer edges must curl towards the limb in order for the cuff to expand inwardly toward the limb. Based on testing done by the inventors of the current invention, the stiff proximal and distal edges of such cuffs tend to kink and buckle inwards towards the limb, presenting a potential chafing and pinching hazard to the patient. Furthermore the distribution of pressure actually applied to the limb is more likely to be uneven due to the resulting kinks. Testing done by the inventors of the current invention also shows that substantially higher pressures are required in the Oak Medical cuff to occlude blood flow in a typical limb compared to other prior art cuffs. Thus, Eaton""s teachings in the ""582 patent and the Oak Medical cuff are examples of prior-art cuffs having simplified physical characteristics that reduce the cost of manufacture but that also reduce the safety and reliability of blood flow occlusion due to the stiff cuff edges. No prior art is known to the inventors of the current invention in which a stiffened portion along the middle of the outer layer (but not extending the full width of the bladder) is continuous along the full length of the cuff and passes through the bladder end seals, thereby allowing a lower cost continuous manufacturing method utilizing a substantially constant cross-section strip to form the outer layer of the cuff.
In certain embodiments of tourniquet cuffs described by Spence in U.S. Pat. No. 5,733,304, in commercial products manufactured in accordance with its teachings (xe2x80x98Color Cuff IIxe2x80x99 sterile disposable tourniquet cuffs, InstruMed Inc., Bothell Wash.) and certain embodiments of tourniquet cuffs described by Goldstein in U.S. Pat. No. 5,411,518, a stiffener is placed in the inflatable bladder but not secured to the outer layer of the bladder or any other portion of the cuff. With this arrangement the stiffener may lie against the inner or outer layer of the bladder when the cuff is inflated and therefore may not restrict outward expansion of the outer layer. Furthermore the stiffener as shown in the ""304 patent and the ""518 patent may shift in the bladder and block the gas passageway entering the bladder, preventing proper inflation or deflation of the cuff and thereby posing a hazard to the patient. Note also that in these cuffs the stiffener does not carry any circumferential tensile loads when the cuff is inflated.
Tourniquet cuffs described by Guzman in European patent application EP1016379A1 and commercial products manufactured in accordance with its teachings (xe2x80x98Comforter(trademark) Disposable Gel Cuffxe2x80x99, DePuy Orthopaedics Inc) include first and second cavities formed by at least three layers of material. The first cavity lies between the limb and the second cavity, is filled with a gel-like material, and is not pressurized at any time during use of the cuff. The second cavity is an inflatable bladder which is pressurized to occlude blood flow in the limb, as in typical pneumatic tourniquet systems. In the xe2x80x98Comforter(trademark)xe2x80x99 cuffs the two cavities have the same perimeter and are formed by a continuous seal joining the three layers of material. The three material layers each have a uniform thickness and stiffness, and there is no stiffener in these cuffs. The purpose of the gel-like material is to more evenly distribute the pressure applied by the cuff to the patient""s limb and therefore be more comfortable for the patient. However, adding the gel layer leads to a substantially thicker cuff compared to other prior art cuffs, which may lead to major variations in the pressure applied to the limb in the overlapping region. The inventors of the current invention have tested various prior art cuffs and found that greater cross sectional thickness causes greater pressure discontinuities in the region of the overlap. In particular, the pressure actually applied to the limb in the region of the overlap could be much less than the inflation pressure of the cuff, thus creating low pressure pathways longitudinally through which arterial blood could enter the limb. Furthermore, a thicker cuff leads to a greater difference in circumference between the inner and outer layers when the cuff encircles the limb causing more severe wrinkling of the inner layer as it is forced around a substantially smaller radius than the outer layer. In testing done by the inventors of the current invention, DePuy Gel Cuffs were found to require significantly greater pressures to occlude typical limbs in comparison to other prior art cuffs and were also found to create large pinches and wrinkles in the patient""s skin both at the cuff overlap and around the remaining circumference of the limb. The gel material also significantly increases the amount material in the cuff and the cost and complexity of manufacture. Conversely, as found in testing conducted by the inventors of the current invention, thin cuffs tend to apply more even pressure to the limb and tend to wrinkle less along the inner layer when encircling the limb. If desired and if the extra cost is warranted, corresponding pinches and wrinkles in the patient""s skin under the cuff may be more effectively prevented by use of a limb protection sleeve specifically designed for use with the cuff as described by McEwen in U.S. patent application Ser. No. 09/378,034 filed Aug. 20, 1999.
Similarly the tourniquet cuff described by Robinette-Lehman in U.S. Pat. No. 4,635,635 and commercial products manufactured in the past in accordance with its teachings (xe2x80x98Banana Cuffxe2x80x99 sterile disposable tourniquet cuffs, Zimmer Arthroscopy Systems, Englewood Colo.) are made of five layers of material including bladder inner and outer layers, a separate sheath of reinforced material containing the stiffener, and an additional inner layer. This construction leads to a thick, complex cuff suffering from the disadvantages described in the preceding paragraph.